Previously there was a TODO to check if we supported ES3 before setting
the conformant bitfield. Now it is done.

BUG=angleproject:1188

Change-Id: Iffe30ebb5538e205695acd619ca17918d8550f3c
Reviewed-on: https://chromium-review.googlesource.com/311690Reviewed-by: Geoff Lang <geofflang@chromium.org>
Tested-by: Corentin Wallez <cwallez@chromium.org>